In the fish industry, fresh fish are filleted and the fillets are tightly packed in cartons and bulk frozen. Frozen blocks of compressed fillets are formed which are processed into consumer-sized portions, usually by sawing the block into cuboids. After cooking by the consumer, these portions have a desirable flaky texture.
However, cuboid portions of frozen fish are not attractive to consumers, as they appear processed or non-natural looking. Hence, processes for shaping portions of fish have been developed, to impart attractive and more natural looking three-dimensional shapes to cuboid fish products, thereby giving a less manufactured appearance.
In GB 2280869, cuboid portions of frozen fish are shaped using high pressure forming. A cuboid portion of frozen fish is placed in a shaped form die and a corresponding shaped upper tool is closed onto the portion in the die and forced therein under hydraulic pressure. The force exerted causes the frozen portion to flow into the cavity in the upper tool, thus taking up the shape of the tooling, both in profile and in the form of the topography of the inside of the surface of the upper tool.
Alternative methods for providing shaped fish products are disclosed in U.S. Pat. No. 5,470,596 and U.S. Pat. No. 4,260,640.
In U.S. Pat. No. 5,470,596, a three-dimensional food product is formed from a flowable, pumpable, raw food material, such as fish, by pumping the material into a mould under pressure.
In U.S. Pat. No. 4,260,640, deep frozen fish is moulded by extrusion under high pressure. The process parameters of pressure and temperature are critically observed to avoid substantial degradation of the structure of the fish.
FR 7225720 discloses a method of moulding fish products to have a natural shape, in which a non-planar moulding surface is used to mould a fish portion. It is mentioned that the fish portion may not completely fill the mould. Moulding is carried out at a temperature in the range -4.5.degree. C.--3.5.degree. C.
Fish muscle comprises myotomes (flakes). Myotomes comprise fibres having a typical diameter of 30 to 200 microns. These fibres comprise myofibrils having a typical diameter of 1 to 2 microns. Myofibrils are built up of many sarcomeres aligned end to end.
Myotomes are connected to each other by myocommata connective tissue, forming myocommata junctions which run in a direction that is approximately 90 degrees to the longitudinal axis of the myotome fibres.
In the methods described above, the shear resulting from pumping, extrusion or high pressure moulding is sufficiently high to cause significant disruption to the fish muscle structure, such that the fibre arrangement is disrupted and the muscle sarcomere structure is deformed. This results in a fish product which has inferior sensory properties, as a result of loss of flakiness, increased toughness and reduced juiciness, particularly after several months of frozen storage.
The present invention seeks to provide a process for making a shaped fish product having improved sensory properties, even after several months of frozen storage.